I think what you're showing here is the safety net that protects them if they make some missteps trying to execute what's covered by other policies. But it seems like the heart of your cancellation is the interpretation of 2.8, i.e. them deciding (probably in an automated way) that the stuff you were serving via API (significant volumes of trading data, I'd gather) does not qualify as web content.
It's definitely an unfriendly combo to have (a) a really ambiguous policy like 2.8 and (b) enforcing via a no-warning cutoff -- even if the two policies have good justifications individually. But I wouldn't jump to the conclusion that part (b) is part of the sales strategy. (Part (a) obviously is meant to incentivize a paid account for applications like yours.)